Effect of postmortem pH on the physical, biochemical, and sensory characteristics of bovine longissimus thoracis et lumborum muscle

From a large feeding trial study consisting of 299 bulls and steers, 15 carcasses exhibited stress-related syndromes manifested by atypical color and pH which were then selected for subsequent analysis. Samples of longissimus thoracis et lumborum muscle with postmortem pH in the range of 5.5–6.9 were subjected to a 14-day aging period at 2°C. Sensory panel tenderness, connective tissue, juiciness, and flavor intensity of high pH (6.4–6.9) meat were significantly different (p <.05) from samples of intermediate pH (6.0–6.1) as well as normal pH (5.5). Muscles at pH 6.0–6.1 were the toughest samples. This was confirmed by Warner–Bratzler shear force (WBSF), residual force, and myofibril fragmentation index. Palatability attributes of normal pH (5.5) samples were significantly different (p <.05) from dark-cutting beef in terms of tenderness and flavor and at the high pH extreme. The increase in WBSF at pH 6.0–6.1, lack of extensive degradation of muscle proteins, and the decreased sarcomere length resulted in tougher meat than low or high pH muscles. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis of meat at the high pH extreme (6.7–6.9) revealed that the breakdown of troponin-T to 30 kD was complete while at intermediate pH (6.0–6.1) was incomplete. In addition, the appearance of a ‘doublet’ on high-molecular-weight resolution gels may also account for the greater tenderness experienced by sensory panelists.